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From: levy.jeffrey@epamail.epa.gov (Jeffrey Levy)
Newsgroups: misc.consumers,sci.engr.heat-vent-ac,rec.autos.tech
Subject: Re: FREON 12 Substitutes - Whadda ya know?
Message-ID: <levy.jeffrey-0909950022260001@playful.mnsinc.com>
Date: 9 Sep 1995 04:16:11 GMT
Lines: 103

In article <2985@sun3.IPSWITCH.COM>, ddl@harvard.edu (Dan Lanciani) wrote:

>typical?  While we are on the subject, what exactly is R500?  It isn't

From memory, R-500 is a blend of CFC-12 and HFC-152a.  It's about 50-50, I
think.  See below for how to be sure.

> in my CGA manual at all, but I'm pretty sure it was used in dehumidifiers
> at one point.  This is fun. :)

That's right.  Both R-500 and CFC-12 are used in dehumidifiers.  R-500 is
also used in a limited number of chillers.

>How are the high-numbered R's assigned?

First, all R-numbers are assigned by the American Society of Heating,
Refrigerating, and Air Conditioning Engineers (ASHRAE).  Specifically,
Standard 34 assigns numbers, flammability ratings (1=nonflammable, 2=lower
flammability, 3=higher flammability), and toxicity ratings (A=lower
toxicity or B=higher toxicity).  There are specific break points for
each.  Example classifications:  all CFCs, R-500, and R-502, plus HFC-134a
and many others are A1 refrigerants:  low toxicity, nonflammable.  Propane
is A3:  low toxicity, highly flammable.

You can contact ASHRAE HQ at (404)636-8400 and order a copy of this
Standard.  The safety classifications are used in Standard 15 to describe
how various refrigerants should be handled, maximum charge sizes, when an
equipment room is needed, etc.  By using the safety classifications, they
avoid having to issue guidance on each individual refrigerant.  Many
states incorporate Standard 15 by reference into building codes.

> (For the low ones, you add 90 and read off C,H,F with the rest being Cl.)

For anything that contains up to 3 carbons (e.g. R-12, R-134a, R-270) and
is a pure fluid (not a blend), there is a unique number that represents
the number of carbons, fluorines, chlorines, and hydrogens.  You're right
about adding 90.

For blends, there are two series, assigned sequentially.  For azeotropic
blends, ASHRAE assigns the 500 numbers.  The first one was R-500, the
second was R-501, etc.  Recent development of substitutes has expanded the
list as high as R-509, I believe.

For zeotropic blends, there is the 400 series, also assigned
sequentially.  No one hears much about R-400, but it was assigned a long
time ago.  All other R-40x blends are substitute refrigerants developed in
the last several years.  So far, they're up to R-411, I think.  (I'm
typing this at home and my copy of the latest Std. 34 is in my office.) 
When different blends of the same composition are classified, they get a
capital letter.  For example, R-401A, R-401B, and R-401C all contain
HCFC-22, HCFC-124, and HFC-152a (again, I'm going on memory here, and if
the components aren't quite right, the methodology is).  But R-401A has a
different mix of those components from R-401B and R-401C.  Those
differences can have marked effects on the properties.

> Oh, and how are the letters assigned?  They seem to be for isomers, but
> is it just a first-come, first-served thing or are there rules?  We
> know R134a is 1,1,1,2-tetraflouroethane; would 1,1,2,2TFE be R134b or
> just R134 or?

For the pure refrigerants, the letter at the end represents an isotope,
and the letter is always lower-case.  Basically, the isotope that is most
symmetrical in its placement of fluorines gets no letter.  So HFC-134
looks like:

   H H
   | |
 F-C-C-F
   | |
   F F

Then, in order of increasing asymmetry, the letters are assigned.  Thus,
HFC-134a is:
   H F
   | |
 H-C-C-F
   | |
   F F

Since there are only two ways you can organize four fluorines and two
hydrogens, that's the end of the HFC-134 family.  But others can have more
arrangements.

Then you get to the three-carbon refrigerants, which can have different
sets of atoms off the middle carbon, in addition to being more or less
symmetrical.  these chemicals get two letters after them:  HFC-236ea vs.
HFC-236fa, for example.  The first letter codes what's connected to the
middle carbon.  That can make a big difference in everything from vapor
pressures to toxicity.

Now, just to add one more bit of info:  each pure refrigerant can be
called either by its R-# (R-12), or by an appropriate prefix (CFC-12). 
Thus, HFC-134a=R-134a, HCFC-141b=R-141b, and HC-270=R-270.  Then, there
are also the chemical names.  For instance, R-270 is known as propane. 
The prefixes are an easy way to determine whether a refrigerant is an
ozone-depleter or not.  If it's a CFC or HCFC, it is.  If it's an HFC or
an HC, it's not.  I'm not positive that HC is a standard prefix, but the
others are.

All of this, plus the safety classifications, is explained in Standard 34.


Gee, I guess I've actually learned a thing or two while evaluating
alternative refrigerants for EPA's SNAP program ;)

Jeffrey Levy
USEPA

 
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